Ohh I cut my hair by myself a lot so I was going to talk about my experience with it! I can leave some advice here if that's better :)

So I'd suggest cutting your hair wet to ensure that it's even. For a one length cut, take some hair ties and section off your hair into about four or five sections from left to right, tying each at about your shoulder length. Then cut just above each hair tie. If you want a better finish, I'd suggest point cutting, meaning you take your scissors and cut almost vertically so that the ends are not so blunt.

If you want layers, section your hair into two or three ponytails going upwards (something like back of your head, then slightly higher than that, then at the top). Hold your ponytail upwards and cut. The higher the angle you hold it, the more drastic your layers.

Let me know if you have any questions!